1. Field of the Invention
The present invention is directed to an incandescent lamp ideally used as a light source of headlights in automobiles, for example.
2. Description of Related Art
Incandescent lamps in conventional automobile headlights have had a film with a high color-temperature conversion comprising a composite oxide of silicon and cobalt or a composite oxide of silicon, cobalt and phosphorous formed on the surface of a glass bulb, as presented in the gazette of Japanese Kokai Publication Hei-9-330685, for example. Such films with high color-temperature conversion absorb the red optical constituents contained at a high level in the light radiated from filament coils, thereby raising the color temperature of the light which is transmitted. They are formed by dipping in a coating liquid of mixed liquids in which the material of the film with high color-temperature conversion is dissolved, followed by drying and baking.
However, the thermal-shock resistance to temperature changes accompanying turning on and off of the lamp is low because the strength of such a film with high color-temperature conversion is low and the resistance to ambient moisture deteriorates at high temperature/humidity. Consequently, such lamps suffer extreme deterioration in long-term use and readily suffer peeling or cracking in a short period of time.
In addition, the thickness of a coating film that is formed in a single dipping operation is low in forming the film with high color-temperature conversion in question. Numerous dipping operations followed by drying/baking operations are required to form a film with high color-temperature conversion having the requisite film thickness. Consequently, the completion of an incandescent lamp that radiates 4000 K of color temperature light that is ideal as an automobile lamp is difficult. Moreover, stress accumulates in films with high color-temperature conversion that are formed by numerous film formation processes because of an increase in the number of layers. That leads to peeling of the layers, and the film with high color-temperature conversion is prone to contamination.
The present invention was completed in light of aforementioned circumstances. The purpose is to provide an incandescent lamp having a film with high color-temperature conversion capable of raising the color temperature of light radiated from an incandescent lamp, thereby increasing the strength of the film with high color-temperature conversion in question in order to prevent cracking or peeling in a simple production method.
The incandescent lamp pursuant to the present invention is formed of a film with high color-temperature conversion containing red optical-absorbent fine particles dispersed in a binder on the surface of a glass bulb. The mean particle diameter of the red optical-absorbent fine particles contained in the film aforementioned high color-temperature conversion is 1 nm to 1000 nm.
In addition, the content proportion of red optical-absorbent fine particles in the film with high color-temperature conversion is 50 to 90 wt %. Furthermore, the binder in the film with high color-temperature conversion should, itself, have red optical-absorption characteristics.
Part of the red optical component of the light from the filament coil transmitted through the film with high color-temperature conversion in question is absorbed due to the action of the red optical-absorbent fine particles dispersed in the binder forming the film with high color-temperature conversion that is formed on the surface of a glass bulb in the incandescent lamp having aforementioned structure. That raises the color temperature resulting in the external radiation of high-purity white light. In addition, the strength of the film with high color-temperature conversion in question is increased because the red optical-absorbent fine particles act as an aggregate in the film with high color-temperature conversion. That results in great durability and permits long-term use.